ATMEGA649 datasheet(181/375 Pages) ATMEL

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ATmega329/3290/649/6490

2552H–AVR–11/06

• Bit 3 – TXENn: Transmitter Enable

Writing this bit to one enables the USART Transmitter. The Transmitter will override nor-

mal port operation for the TxD pin when enabled. The disabling of the Transmitter

(writing TXENn to zero) will not become effective until ongoing and pending transmis-

sions are completed, i.e., when the Transmit Shift Register and Transmit Buffer Register

do not contain data to be transmitted. When disabled, the Transmitter will no longer

override the TxD port.

• Bit 2 – UCSZn2: Character Size

The UCSZn2 bits combined with the UCSZn1:0 bit in UCSRnC sets the number of data

bits (Character SiZe) in a frame the Receiver and Transmitter use.

• Bit 1 – RXB8n: Receive Data Bit 8

RXB8n is the ninth data bit of the received character when operating with serial frames

with nine data bits. Must be read before reading the low bits from UDRn.

• Bit 0 – TXB8n: Transmit Data Bit 8

TXB8n is the ninth data bit in the character to be transmitted when operating with serial

frames with nine data bits. Must be written before writing the low bits to UDRn.

UCSRnC – USART Control

and Status Register n C

• Bit 6 – UMSELn: USART Mode Select

This bit selects between asynchronous and synchronous mode of operation.

• Bit 5:4 – UPMn1:0: Parity Mode

These bits enable and set type of parity generation and check. If enabled, the Transmit-

ter will automatically generate and send the parity of the transmitted data bits within

each frame. The Receiver will generate a parity value for the incoming data and com-

pare it to the UPMn0 setting. If a mismatch is detected, the UPEn Flag in UCSRnA will

be set.

Bit

543

–

UMSELn

UPMn1

UPMn0

USBSn

UCSZn1

UCSZn0

UCPOLn

UCSRnC

Read/Write

R/W

Initial Value

Table 80. UMSELn Bit Settings

UMSELn

Mode

Asynchronous Operation

Synchronous Operation

Table 81. UPMn Bits Settings

UPMn1

UPMn0

Parity Mode

Disabled

Reserved

Enabled, Even Parity

Enabled, Odd Parity

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